The present disclosure relates generally to semiconductor processing equipment and, more particularly, to systems, devices, and methods for delivering contaminant-free, precisely metered quantities of process gases to semiconductor process chambers. Even more particularly, the present disclosure relates to a system and method for dividing a single mass flow into a desired ratio of two or more flows.
The fabrication of semiconductor devices often requires the careful synchronization and precisely measured delivery of as many as a dozen gases to a process chamber. Various recipes are used in the fabrication process, and many discrete processing steps, where a semiconductor device is cleaned, polished, oxidized, masked, etched, doped, metalized, etc., can be required. The steps used, their particular sequence, and the materials involved all contribute to the making of particular devices.
Accordingly, wafer fabrication facilities are commonly organized to include areas in which chemical vapor deposition, plasma deposition, plasma etching, sputtering and other similar gas manufacturing processes are carried out. The processing tools, be they chemical vapor deposition reactors, vacuum sputtering machines, plasma etchers or plasma enhanced chemical vapor deposition, must be supplied with various process gases. Pure gases must be supplied to the tools in contaminant-free, precisely metered quantities.
In a typical wafer fabrication facility the gases are stored in tanks, which are connected via piping or conduit to a gas box. The gas box delivers contaminant-free, precisely metered quantities of pure inert or reactant gases from the tanks of the fabrication facility to a process tool. The gas box, or gas metering system includes a plurality of gas paths having gas metering units, such as valves, pressure regulators and transducers, mass flow controllers and filters/purifiers. Each gas path has its own inlet for connection to separate sources of gas, but all of the gas paths converge into a single outlet for connection to the process tool.
Sometimes dividing the combined process gases equally among multiple process chambers, or among separate portions of a single process chamber, is desired. In such cases, the single outlet of the gas box is connected to secondary flow paths. To insure that the primary flow of the outlet of the gas box is divided equally among the secondary flow paths, flow restrictors are placed in each secondary flow path.
What is still desired, however, is a mass flow ratio system and method for dividing a single flow into a desired ratio of two or more flows. Preferably, the system and method will operate independently of the gas or gases controlled. In addition, the system and method preferably will not disturb the performance of any upstream mass flow controllers.
Accordingly, the present disclosure provides a system for dividing a single mass flow into two or more secondary mass flows of desired ratios. The system includes an inlet adapted to receive the single mass flow and at least two secondary flow lines connected to the inlet. Each flow line includes a flow meter measuring flow through the flow line and providing a signal indicative of the measured flow, and a valve controlling flow through the flow line based upon receiving a signal indicative of desired flow rate.
The system also includes a user interface adapted to receive at least one desired ratio of flow, and a controller connected to the flow meters, the valves, and the user interface. The controller is programmed to receive the desired ratio of flow through the user interface, receive the signals indicative of measured flow from the flow meters, calculate an actual ratio of flow through the flow lines based upon the measured flow, and compare the actual ratio to the desired ratio. The controller is also programmed to calculate the desired flow through at least one of the flow lines if the actual ratio is unequal to the desired ratio, and provide a signal indicative of the desired flow to at least one of the valves.
The present disclosure also provides a method for dividing a single mass flow into two or more secondary mass flows of desired ratios. The method includes dividing a single mass flow into at least two secondary flow lines, measuring mass flow through each flow line, receiving at least one desired ratio of mass flow, and calculating an actual ratio of flow through the flow lines based upon the measured flows. If the actual ratio does not equal the desired ratio, the method also includes calculating a desired flow through at least one of the flow lines, and regulating the actual flow in that flow line to the desired flow.
The system and method of the present disclosure provide the benefit of operating independently of the gas or gases controlled. In addition, the system and method do not disturb the performance of any upstream mass flow controllers.
These and other features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiments, which are illustrated in the attached drawing figures.